Synthetic observations using POLARIS: an application to simulations of massive prestellar cores

Astrophysics and Space Science - Dynamical evolution of galaxies is a complex process, especially the centers. Gravitationally coupled gas and stellar discs have been observed to coexist in the...     

Differential host use affects fecundity of the gastropod Crepidula onyx

For epibiotic or symbiotic marine invertebrates, alternative host species may differ substantially in quality, and under some circumstances such differences in host quality may lead to the evolution of increased host specificity. However, the fitness consequences of alternative hosts for epibiotic or symbiotic marine invertebrates have rarely been quantified. In Southern California, the gastropod Crepidula onyx is often found as an epibiont on either bay mussels (Mytilus galloprovincialis) or cone snails (Conus californicus). These hosts differ greatly in maximum size, with possible effects on size at sex change and final size in Cr. onyx, and thus on fecundity. Further, Cr. onyx on the two hosts differ in shell shape, possibly affecting the size of the ctenidium, which Cr. onyx uses for suspension feeding. We examined these potential effects of host use on fitness components in Cr. onyx. Epibionts on mussels reached much larger average sizes than did those on cone snails; further, epibionts on mussels often completed sex change at much larger sizes than did those on cone snails. On average, mussel epibionts had threefold higher average fecundities than did cone snail epibionts. Although there was a slight difference in shell shape between epibionts on the two host species, there was no difference in the scaling of ctenidium area with body size for Cr. onyx from the two hosts. The large average differences in fecundity in epibionts associated with the two alternative hosts suggests that there may be strong selection on host choice at larval settlement.     

Transformation of Aerosol Chemical Properties due to Transport Over a City

The change of the chemical composition of the near-ground level atmospheric aerosol was studied during two summer episodes by a Lagrangian type of experimental approach. Bulk and single-particle chemical analyses of ions and elements in the particulate phase were deployed. N(-III) and N(V) components were also measured in the gas-phase. The measurements were completed by particle size distributions.Secondary inorganic aerosols (SIA) and fine particles of ≈0.2–0.4 μm size were still elevated 50 km downwind of the city. The direct comparison of transport over the city in contrast to transport over the surrounding areas showed that SIA was formed from emission from the city within less than 3 h. Relative increases, i.e., enrichment during transport were observed for primary and secondary aerosol components. The degree of mixing on the individual particle level increased significantly during transport in the area. In particular, newly emitted carbonaceous particles became internally mixed within hours with pre-existing sulphate particles. Mostly due to secondary aerosol formation the average particle size (mass median diameter) of major constituents of the aerosol was significantly decreased while being transported over 13 h. Given recent insights which link fine particles number and mass concentrations with health risks, the results suggest that rural populations in areas which frequently are located within an urban plume might run an elevated health risk relative to populations in areas not affected by urban plumes.     

Enhancement and suppression of urban heat plumes over Johannesburg

Observations of the atmospheric temperature structure over Johannesburg have revealed the existence of both well-developed and suppressed heat plumes. Suppressed plumes appear to be associated with the incidence in a stable atmosphere of positive wind shear and well-developed katabatic flow away from the city. A localised cool region in the atmosphere above the central city is invariably associated with suppressed plume development. A tentative identification of wind shear and katabatic flow as the major influences on such structures is strengthened by the observation that during conditions of negative windshear and reduced katabatic advection, significant heat plumes are developed. It is at present not possible to assess the extent to which the observations and causative processes are site-specific.Visiting from Bar-Ilan University, Israel.     

Magnesium in the marine sedimentary environment: Mg---NH4 ion exchange

The release of exchangeable Mg in marine sediments from displacement by ammonium ions was estimated by way of experimentally determining the parameters that govern this ion-exchange equilibrium on solid geochemical phases: smectite, humic acid, illite and opal.

We showed that: (a) both the conditional selectivity constant as well as the solid concentration are important parameters in determining the relative contribution of ammonium-exchangeable Mg from smectite, organic matter, illite and opal; and (b) that, except in the cases where opal or organic matter concentrations are very high, the clays are the dominant carrier phases for labile Mg which is exchangeable by ammonium.

A model, based on the sum of the contributions from the major geochemical phases present in the sediment reliably predicts the amount of Mg released by exchange with ammonium in marine sediments.     

Rare earth distributions in clay minerals and in the clay-sized fraction of the Lower Permian Havensville and Eskridge shales of Kansas and Oklahoma

The REE (rare earth element) content of a wide variety of clay mineral groups have been analyzed using radiochemical neutron activation and have been found to be quite variable in absolute REE content (range of ∑REE = 5.4–1732) and less variable in relative REE content (range of chondritenormalized La/Lu = 0.9–16.5). The variable REE content of the clay mineral groups is probably determined by the REE content of the source rock from which the clay mineral was derived and not from the separate minerals in the rock.The clay-sized fractions of the Havensville and Eskridge shales of Kansas and Oklahoma have similar relative REE distributions and identical negative Eu anomaly size as the composite of NAS (N. American shales), but an absolute REE content (range of ∑REE = 46–348) that may differ significantly from the composite of NAS. The clay-sized fraction of samples from any given outcrop did not vary much in absolute or relative REE content, but samples from northern Oklahoma, probably composed of continental to near-shore marine sediments, have higher absolute REE contents and higher La/Lu ratios than samples of marine deposits in Kansas (e.g. mean ∑REE in Oklahoma = 248; mean ∑REE in Kansas = 69–116). The differencess in the REE content between samples in Oklahoma and Kansas may be caused by chemical weathering processes in the source area, exchange reactions in the environment of deposition, or diagenesis and do not appear to be a result of the different clay minerals.Most samples have Eu anomalies relative to chondrites (range of Eu/Sm ratios of samples = 0.035–1.17; chondrites = 0.35). Some montmorillonites and kaolinites are anomalous in Eu relative to the NAS (range of Eu/Sm ratios of samples = 0.056–0.21; NAS = 0.22). These anomalies may be inherited from source rocks with Eu anomalies originally produced by igneous processes, or they may be produced by chemical weathering processes in the source area.     

Assessment of integrity and geochronology of archaeological sites using amino acid racemization in land snail shells: Examples from central Texas

Detailed racemization analyses were carried out on samples of the land snail Rabdotus mooreanus from archaeological sites at Fort Hood, in central Texas. D -alloisoleucine/L -isoleucine (A/I) values were determined for 260 individual shells from 29 proveniences, including sites in alluvium, colluvium, and rockshelters, as well as burned rock middens. A/I values show a good correlation with radiocarbon age, and so provide reasonably precise estimates of ages. Analyses indicate the presence of redeposited material in a large number of proveniences. These result from sedimentary processes involved in burial of the sites as well as from later disturbance (aboriginal or recent) of site stratigraphy. Because amino acid racemization analyses are relatively easy to carry out, this method lends itself to very detailed chronostratigraphic analyses of archaeological sites, thus permitting assessment of site integrity and assisting in the interpretation of site formation processes. © 1996 John Wiley & Sons, Inc.     

Looking for a massive KeV pseudo-scalar in gamma ray bursts

Looking for repetitive signals within a γ burst may provide evidence for a massive KeV pseudo-scalar coupled to electromagnetism. We study the possible signatures that may occur for pseudo-scalar electromagnetic propagation and outline possible probes to the pseudo-scalar mass as well as its coupling to electromagnetism.     

Combining astrometry with the light‐time effect: The case of VW Cep, ζ Phe and HT Vir

Three eclipsing binary systems with astrometric orbit have been studied. For a detailed analysis two circular‐orbit binaries (VW Cep and HT Vir) and one binary with an eccentric orbit (ζ Phe) have been chosen. Merging together astrometry and the analysis of the times of minima, one is able to describe the orbit of such a system completely. The O – C diagrams and the astrometric orbits of the third bodies were analysed simultaneously for these three systems by the least‐squares method. The introduced algorithm is useful and powerful, but also time consuming, due to many parameters which one is trying to derive. The new orbits for the third bodies in these systems were found with periods 30, 221, and 261 yr, and eccentricities 0.63, 0.37, and 0.64 for VWCep, ζ Phe, and HT Vir, respectively. Also an independent approach to compute the distances to these systems was used. The use of this algorithm to VW Cep gave the distance d = (27.90 ± 0.29) pc, which is in excellent agreement with the previous Hipparcos result. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)